The present invention concerns a biodegradable sheet for culturing sewage denitrifiers that multiply spontaneously. Denitrifiers are bacteria and other microbes that decompose nitrates.
A biodegradable culture medium (polyhydroxybutyrate plus polyhydroxyvalerate) derived from poly-.beta.-hydroxybutyric acid and poly-.beta.-hydroxyvaleric acid and intended for biological nitrate elimination (denitrification) is described by Wolf-Rudiger Muller in the article "Abwasser mit zerkleinertem Kunststoff reinigen" in Umwelt, Vol. 20 (1990). Sheets of the material are obtained biotechnologically in fermenters by bacterial metabolism. Colonization with populations of denitrifiers and the potential for denitrification without introducing other, foreign, organic hydrogen-and-carbon donors has been studied. The nitrogen-oxide level subsequent to denitrification has never been investigated.
Since the microbes can obtain hydrogen and carbon from the sheet, there is no need of the toxic methyl alcohol as a donor. This feature is particularly desirable from the aspect of rendering the water potable. The material also makes it possible to carry out denitrification in a column or basin subsequent to filtration and nitrification as a stage in the treatment of sewage and underground water. The process involves intermediate accommodation of the used substrate in a column to allow fresh denitrifier populations to grow.
One drawback of this system is the expense incurred in biosynthesizing the substrate, which prevents its extensive use. Another is that not very much polyhydroxybutyrate plus polyhydroxyvalerate (PHB-PHV) can be biotechnologically produced in fermenters per year. Again, the systems can be processed only into sheets with a limited and unexpandable surface and hence a limited capacity for absorbing denitrifiers.